Process for preparation of 1-benzylimidazole compound
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a process for preparing a 1-benzylimidazole compound by benzylation of a 1-unsubstituted imidazole, and also to a novel 1-benzylimidazole compound. The 1-benzylimidazole compound is valuable as a curing agent and a curing promoter for a polyepoxy resin. 
     (2) Description of the Related Art 
     A process for reacting a 1-unsubstituted imidazole compound with benzyl chloride, cooperating with an HC acceptor in an appropriate solvent having no active hydrogen atom is known [see, for example, Recl. Trev. Chim. Pays-Bas, Vol. 91, No. 12, 1383-1392 (1972)]. 
     This benzylation process, however, involves the following problems. Namely, the 1-imidazole compound formed by the reaction between the 1-unsubstituted imidazole compound and benzyl chloride is likely to react further with unreacted benzyl chloride to form a 1,3-dibenzyl imidazolium chloride compound, and therefore, the unnecessary imidazolium chloride is formed as a by-product in a large quantity. Moreover, benzyl chloride is difficult to handle because of the lacrimatory property. 
     SUMMARY OF THE INVENTION 
     Under this background, we made research with a view to solving the above-mentioned problems, and as a result, it was found that a 1-benzylimidazole compound can be obtained at a high efficiency by heating to react a 1-unsubstituted imidazole compound with benzyl alcohol in the presence of a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof or a lower alkyl ester thereof and neutralization of the reaction product with an alkali. 
     It was also found that a 1-benzylimidazole compound is similarly obtained by reactng a 1-unsubstituted imidazole compound with a benzyl ester of a carboxylic acid and neutralizing the reaction product with an alkali. 
     We have now completed the present invention based on these findings. 
     More specifically, in accordance with one aspect of the present invention, there is provided a process for the preparation of a 1-benzylimidazole compound represented by the following general formula: ##STR3## wherein R 2  represents a lower alkyl group or phenyl group, and R 4  represents a hydrogen atom or a methyl group, 
     which comprises heating and to react a 1-unsubstituted imidazole compound represented by the following general formula: ##STR4## wherein R 2  and R 4  are as defined above, with benzyl alcohol in the presence of a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof or a lower alkyl ester thereof, and neutralization of the reaction product with an alkali. 
     In accordance with another aspect of the present invention, there is provided a process for the preparation of a 1-benzylimidazole compound represented by the following general formula: ##STR5## wherein R 2  represents a lower alkyl group or a phenyl group, and R 4  represents a hydrogen atom or a methyl group, 
     which comprises heating to react a 1-unsubstituted imidazole compound represented by the following general formula ##STR6## 
     wherein R 2  and R 4  are as defined above, with a benzyl ester of a carboxylic acid and neutralization of the reaction product with an alkali. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The preparation process of the present invention is represented by the following reaction formulae: ##STR7## wherein R 2  represents a lower alkyl group or a phenyl group, R 4  represents a hydrogen atom or a methyl group, and R represents a carboxylic acid residue. 
     In the reaction of formula I, the carboxylic acid, carboxylic anhydride or benzyl or lower alkyl ester thereof is used in an amount of 0.01 to 1.0 mole, preferably 0.05 to 0.4 mole, per mole of the imidazole compound. Benzyl alcohol is used in an amount of 1.05 to 1.5 moles per mole of the imidazole compound. The reaction temperature is 200° to 300° C., preferably 230° to 260° C. In this case, the reaction is completed within 4 hours. The reaction can be carried out under atmospheric pressure or under such a reduced pressure that benzyl alcohol is not distilled. Water formed by the reaction is removed from the reaction system in the form of an azeotrope (boiling point=98° C.) by distillation. In order to remove a small amount of water that remains in the reaction mixture, the pressure is reduced to about 600 mmHg at the state where the reaction is sufficiently advanced, or scavenging is carried out by using an inert gas. 
     In the reaction of the present invention, a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof and a lower alkyl ester thereof exert the catalytic action. This is a novel finding. 
     After an alkali hydroxide has been added to the reaction mixture in an amount sufficient to effect the neutralization, distillation is carried out under a reduced pressure, a crude intended 1-benzylimidazole compound can be obtained. 
     After an alkali hydroxide has been added to the crude compound in a molar quantity corresponding to the unreacted imidazole compound, distillation under a reduced pressure is carried out again, the intended compound substantially free of the unreacted imidazole compound can be obtained. 
     The carboxylic acid, the carboxylic anhydride and the benzyl ester thereof, are benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, isophthalic acid, terephthalic acid, succinic acid, maleic acid, adipic acid, and anhydrides and benzyl esters thereof (inclusive of semiesters of polycarboxylic acids). 
     The benzyl ester of the carboxylic acid is obtained by heating to react benzyl alcohol with a corresponding carboxylic anhydride or carboxylic acid. Accordingly, in carrying out the present invention, a carboxylic acid and benzyl alcohol can be used in combination instead of the carboxylic acid ester itself. 
     It is known that a lower alkyl ester of a carboxylic acid is easily ester-exchanged with benzyl alcohol to form a benzyl ester by heating (the low alkyl alcohol is distilled out of the reaction system because of its lower-boiling point). 
     Accordingly, a lower alkyl ester of a carboxylic acid, such as a methyl ester, an ethyl ester, a propyl ester, an isopropyl ester or a butyl ester can be used, in carrying out the present invention, respectively. 
     In the process represented by reaction formula [II], the benzyl ester of the carboxylic acid should be used in an amount equal to, or slightly larger than, the equivalent amount of the imidazole compound. The reaction temperature is generally 200° to 300° C. and preferably 230° to 260° C. In this case, the reaction is completed within 4 hours. After the carboxylic acid component of the reaction mixture has been neutralized with an alkali, an organic solvent (such as acetone) is added to the reaction mixture, and the mixture is filtered and the filtrate is subjected to distillation under a reduced pressure, whereby a crude intended 1benzylimidazole compound can be obtained. An alkali hydroxide is added to the crude intended compound in a molar quantity corresponding to the unreacted imidazole compound and distillation under a reduced pressure is carried out again, whereby an intended compound substantially free from the unreacted imidazole compound is obtained. 
     As the typical carboxylic acid used for the synthesis of the benzyl ester, there can be mentioned benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, isophthalic acid, terephthalic acid, maleic acid and adpic acid, and acid anhydrides thereof. 
     The benzyl ester (inclusive of a semiester) of the carboxylic acid can be obtained by heating benzyl alcohol with a corresponding carboxylic anhydride or carboxylic acid while distilling water formed by the reaction from the reaction system. 
     Typical imidazole compounds used in the present invention include 2-methylimidazole (hereinafter referred to as &#34;2MZ&#34;), 2-ethylimidazole (hereinafter referred to as &#34;2RZ&#34;), 2-isopropylimidazole (hereinafter referred to as &#34;2IZ&#34;), 2-phenylimidazole (hereinafter referred to as &#34;2PZ&#34;), 2-ethyl-4-methylimidazole (hereinafter referred to as &#34;2E4MZ&#34;), and 2-phenyl-4-methylimidazole (hereinafter referred to as &#34;2P4MZ&#34;). 
     The properties of 1-benzylimidazoles prepared according to the process are described below. Incidentally, 1-benzyl-2-ethylimidazole, 1-benzyl-2-ethyl-4(5)-methylimidazole are novel compounds. 
     1-Benzyl-2-methylimidazole ##STR8## 
     Neutral colorless crystal having a melting point of 48° to 52° C. (hexane) and being hardly soluble in water but easily soluble in alcohols, acetone and benzene, TLC (silica gel, methanol, I 2  coloration): 
     Rf=0.60 to 0.75 
     IR:  KBr   cm   -1  3400(19), 3030(23), 1675(30), 1610(35), 
     1590(37), 1530(29), 1500(24), 1475(26), 
     1455(24), 1430(22), 1360(28), 1290(25), 
     1205(47), 1160(32), 1135(30), 1080(38), 
     1035(33), 990(30), 932(47), 850(42), 
     730(21), 700(25), 680(29) 
     Each parenthesized value indicates the percent transmission. 
     1-Benzyl-2-ethylimidazole ##STR9## 
     Weakly basic colorless liquid having a boiling point (bp24) of 186° to 191° C. can being insoluble in water but easily soluble in alcohols, acetone and chloroform. 
     TLC(silica gel, acetone, I 2  coloration): 
     Rf=0.32 to 0.45 
     IR νliquid film 3110(44), 3070(45), 3040(42), 
     cm -1  2980(32), 2940(37), 2880(45), 
     1603(48), 1520(43), 1495(23), 
     1451(24), 1428(26), 1370(45), 
     1353(41), 1330(47), 1273(34), 
     1180(53), 1150(43), 1120(48), 
     1070(42), 1040(42), 1025(45), 
     960(54), 910(53), 832(55), 
     720(20), 688(33) 
     Each parenthesized value indicates the percent transmission. 
     NMR(CDCl 3 ): δ7.0-7.4, m, 5H; 6.98, S, 1H and 6.82 
     S, 1H; 5.04, S,2H; 2.63, q(J=7hz), 
     2H; 1.28, t(J=7Hz), 3H 
     Mass m/e: 186, 95, 91, 65 
     1-Benzyl02isopropylimidazole ##STR10## 
     Basic light-yellow liquid having a boiling point (bpl0) of 166° to 168° C. and being insoluble in water but easily soluble in alcohols, acetone and chloroform. TLC (silica gel, CHC 3  /MeOH=9/1, B.T.B. coloration): 
     RF =0.60 to 0.80 
     IR: νliquid film cm -1  3100(52), 3060(53), 3030(48), 
     cm -1  2960(37), 2920(41), 2860(47), 
     1600(59), 1510(53), 1480(39), 
     1450(39), 1350(45), 1270(41), 
     1162(51), 1145(51), 1060(42), 
     1010(55), 710(41), 680(44) 
     Each parenthesized value indicates the percent transmission. 
     NMR(CDCl 3 ): δ7.0-7.4, m, 5H(phenyl grup); 
     7.0, S, 1H and 6.8, S, 1H(4- and 5-positions); 
     5.1, S, 2H(methylene 
     group); 2.9, septet, 1H; 1.2, d, 6H 
     Mass m/e: 201(M +  +1), 200(M + ), 185(M +  -CH 3 ), 
     157(M +  -isopropyl), 109(M +  -benzyl), 
     91(benzyl), 65 
     1-Benzyl-2-phenylimidazole ##STR11## 
     Neutral colorless crystal having a melting point of 51° to 53° C. (hexane) and being insoluble in water and hexane but easily soluble in alcohols, acetone and benzene. 
     TLC (silica gel, acetone, I 2  coloration): 
     RF=0.65 to 0.73 
     IR: νKBr 3100(38), 3055(35), 3025(36), 2920(40), 
     cm -1  (1600(42), 1490(29), 1462(25), 1447(26), 
     1409(26), 1350(40), 1265(32), 1170(49), 
     1150(50), 1118(41), 1065(40), 1020*47), 
     1010(39), 990(51), 947(52), 903(46), 
     935(53), 760(28), 700(22), 682(16) 
     Each parenthesized value indicates the percent transmission. 
     NMR(CDCl 3 ): δ7.54, (J=6Hz), 2H(imidazole 
     ring); 7.4-6.9, m, 10H (phenyl); 5.21, 
     S, 2H(methylene) 
     Mass m/e: 235(M +  +1), 234(M + ), 143, 91, 76, 65 
     1-Benzyl-2-ethyl04(5)-methylimidazole ##STR12## 
     Resin colorless crystal having a molting point of to 72° C. (toluene) and being insoluble in water but easily soluble in alcohols, acetone and chloroform. TLC (silica gel, methanol, I 2  coloration): 
     Rf=0.60 to 0.70 
     IR: νliquid film 3360(31), 3030(34), 2970(20), 
     cm -1  2930(22), 2870(35), 1950(65), 
     1810(65), 1650(58), 1600(53), 
     1570(50), 1493(25), 1450(18), 
     1420(19), 1378(44), 1350(40), 
     1320(47), 1295(34), 1160(51), 
     1065(38), 1025(46), 1005(54), 
     980(60), 795(57), 725(22), 
     690(24) 
     NMR(CDCl 3 ): δ7.35-7.28, m, 3H; 7.05 and 6.91, m, 
     2H (inclusive of isomers); 6.75 and 
     6.51, S, 1H (proton of imidazole ring, 
     inclusive of isomers); 
     5.01 and 5.00, S, 2H (methylene, 
     inclusive of isomers); 2.60, q, 2H 
     methylene of ethyl); 2.20 and 2.07, 
     S, 3H (inclusive of isomers); 1.25, t, 
     3H (terminal methyl) 
     Mass m/e: 201(M +  +1), 200(M + ), 185(M +  -methyl), 
     171 (M +  -ethyl), 134, 109 (M +  -benzyl), 
     92, 91, 89, 76, 65, 51, 42, 40 
     1-Benzyl-2-phenyl-4(5)-methylimidazole ##STR13## 
     Neutral light-yellow crystal having a melting point of 62° to 64° C. (acetone) and being insoluble in water but easily soluble in alcohols, acetone and chloroform. TLC (silica gel, MeOH, I 2  coloration): 
     Rf=0.80 to 0.90 
     IR νliquid film 3660(50), 3380(28), 3070(23), 
     cm -1  3040(25), 2950(29), 2920(25), 
     1960(60), 1890(63), 1810(62), 
     1640(51), 1605(35), 1570(17), 
     1495(17), 1470( 9), 1450( 6), 
     1405( 6), 1355(20), 1300(29), 
     1250(51), 1160(30), 1073(31), 
     1021(26), 915(48), 840(59), 
     800(38), 765( 9), 725( 9), 
     705(10), 690( 4) 
     NMR(CDCl 3 ): δ7.56-7.46 and 7.40-7.23 and 7.10-7.00, 
     m, 10H; 6.64, S, 1H 
     (imidazole ring); 5.10, B, 2H 
     (methylene); 2.24, S, 3H (methyl) 
     Mass m/e: 249(M +  +1), 248(M + ), 158, 157, 
     101, 91, 59, 58, 56, 55, 46, 45, 
     43, 41, 39, 31 
    
    
     The present invention will now be described in detail with reference to the following examples that by no means limit the scope of the invention. 
     EXAMPLES 1 THROUGH 25 
     A predetermined amount of a carboxylic acid, a carboxylic anhydride or a lower alkyl ester of a carboxylic acid is mixed with 0.1 mole of a 1-unsubstituted imidazole and 0.11 mole of benzl alcohol, and heating reaction was carried out under predetermined conditions. Then, an alkali was added to the reaction mixture to effect neutralization and salting-out. The formed oil layer was separated and collected, and the extract was subjected to distillation under a reduced pressure singly or in the presence of NaOH to obtain a crude intended 1-benzylimidazole compound. The experimental conditions and obtained results are shown in Table 1. 
     Incidentally, runs where benzyl alcohol was first esterified with a carboxylic acid, a 1-unsubstituted imidazole compound was added to the reaction system and heating reaction was then carried out are indicated by &#34;esterification precedent&#34; in column &#34;Remarks&#34;. 
     When each of the obtained crude intended compounds was examined by TLC (silica gel/acetone), it was found that each crude intended compound contained only a very small amount of the unreacted imidazole. 
     
                                           TABLE 1                                 
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                            Reaction                                      
Example                     Temperature                                   
No.  Imidazole                                                            
            Carboxylic Acid                                               
                       (mole)                                             
                            (°C.)                                  
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 1   2EZ    trimellitic acid                                              
                       (0.005)                                            
                            250                                           
 2   2EZ    trimellitic acid                                              
                       (0.005)                                            
                            250                                           
 3   2EZ    trimellitic acid                                              
                       (0.005)                                            
                            250                                           
 4   2EZ    trimellitic acid                                              
                       (0.01)                                             
                            250                                           
 5   2EZ    trimellitic acid                                              
                       (0.02)                                             
                            250                                           
 6   2EZ    trimellitic acid                                              
                       (0.03)                                             
                            250                                           
 7   2EZ    trimellitic acid                                              
                       (0.04)                                             
                            250                                           
 8   2EZ    trimellitic anhydride                                         
                       (0.01)                                             
                            250                                           
 9   2EZ    phthalic acid                                                 
                       (0.03)                                             
                            250                                           
10   2EZ    phthalic anhydride                                            
                       (0.01)                                             
                            250                                           
11   2EZ    isophthalic acid                                              
                       (0.01)                                             
                            250                                           
12   2EZ    isophthalic acid                                              
                       (0.03)                                             
                            250                                           
13   2EZ    terephthalic acid                                             
                       (0.01)                                             
                            230≈260                               
14   2EZ    pyromellitic acid                                             
                       (0.03)                                             
                            250                                           
15   2EZ    benzoic acid                                                  
                       (0.03)                                             
                            250                                           
16   2EZ    succinic acid                                                 
                       (0.01)                                             
                            250                                           
17   2EZ    malic acid (0.03)                                             
                            250                                           
18   2EZ    adipic acid                                                   
                       (0.03)                                             
                            250                                           
19   2EZ    monomethyl phthalate                                          
                       (0.01)                                             
                            250                                           
20   2MZ    trimellitic acid                                              
                       (0.02)                                             
                            250                                           
21   2MZ    terephthalic acid                                             
                       (0.03)                                             
                            250                                           
22   2IZ    phthalic anhydride                                            
                       (0.01)                                             
                            250                                           
23   2E4MZ  phthalic anhydride                                            
                       (0.01)                                             
                            250                                           
24   2PZ    phthalic anhydride                                            
                       (0.01)                                             
                            250                                           
25   2P4MZ  trimellitic acid                                              
                       (0.01)                                             
                            250                                           
__________________________________________________________________________
Example                                                                   
     Reaction                                                             
            Post Treatment                                                
                         Yield                                            
No.  Time(hours)                                                          
            Conditions   (mole %)                                         
                              Remarks                                     
__________________________________________________________________________
 1   4      NaOH 1.6 g, water 20 ml                                       
                         76.3                                             
 2   4      not neutralized                                               
                         72.0                                             
 3   4      in the presence of                                            
                         84.0 esterification                              
            NaOH 1.0 g        precedent                                   
 4   4      in the presence of                                            
                         68.0                                             
            NaOH 1.2 g                                                    
 5   4      NaOH 1.6 g, water 20 ml                                       
                         76.3                                             
 6   3.5    NH.sub.4 OH  74.7                                             
 7   4      NaOH 1.6 g, water 30 ml                                       
                         69.3                                             
 8   4      in the presence of                                            
                         65.0                                             
            NaOH 1.6 g                                                    
 9   3      NH.sub.4 OH  87.6                                             
10   4      in the presence of                                            
                         88.0                                             
            NaOH 1.0 g                                                    
11   10     in the presence of                                            
                         76.9 esterification                              
            NaOH 1.2 g        precedent                                   
12   6      NH.sub.4 OH  76.0                                             
13   8      in the presence of                                            
                         74.7                                             
            NaOH 1.0 g                                                    
14   3      NH.sub.4 OH  74.0                                             
15   4      NH.sub.4 OH  87.6                                             
16   4      in the presence of                                            
                         74.0                                             
            NaOH 1.0 g                                                    
17   3.5    NH.sub.4 OH  71.0                                             
18   3      NH.sub.4 OH  55.0                                             
19   4      in the presence of                                            
                         76.9                                             
            NaOH 1.2 g                                                    
20   3.5    NH.sub.4 OH  59.3                                             
21   5      NH.sub.4 OH  83.7                                             
22   4      in the presence of                                            
                         84.0                                             
            NaOH 0.8 g                                                    
23   4.5    in the presence of                                            
                         67.5 esterification                              
            NaOH 1.0 g        precedent                                   
24   5      in the presence of                                            
                         81.0                                             
            NaOH 1.0 g                                                    
25   5      in the presence of                                            
                         74.0                                             
            NaOH 1.0 g                                                    
__________________________________________________________________________
 
    
     EXAMPLES 26 THROUGH 34 
     A benzyl ester of a carboxylic acid was added to 0.1 mole of a 1-unsubstituted imidazole compound in an amount equivalent to the amount of the imidazole compound (3.3 equivalents), and heating reaction was carried out under predetermined conditions and the reaction mixtue was subjected to neutralization and salting-out wih an alkali. The formed oil layer was separated and collected. Then, neutralization was carried out according to need, and the mixture was dried to the solid under a reduced pressure, extracted with methanol and subjected to distillation under a reduced pressure to obtain a crude intended 1-benzylimidazole compound. The experimental conditions and obtained results are shown in Table 2. When the crude intended compound was examined by the thin layer chromatography in the same manner as in the preceding examples, it was found that only a very small amount of the unreacted imidazole was contained as an impurity. 
     
                                           TABLE 2                                 
__________________________________________________________________________
                    Reaction                                              
                           Reaction                                       
Example    Benzyl Ester of                                                
                    Temperature                                           
                           Time Yield                                     
No.  Imidazole                                                            
           Carboxylic Acid                                                
                    (°C.)                                          
                           (hours)                                        
                                (mole %)                                  
                                     Remarks                              
__________________________________________________________________________
26   2EZ   monobenzyl                                                     
                    250    4    63   drying to solid and                  
           phthalate                 extraction with metha-               
                                     nol after neutralization             
27   2EZ   dibenzyl 250    2    50   drying to solid and                  
           phthalate                 extraction with metha-               
                                     nol after neutralization             
28   2EZ   dibenzyl 250    4    72   neutralization and                   
           maleate                   salting-out                          
29   2EZ   dibenzyl 250    4    78   neutralization and                   
           adipate                   salting-out                          
30   2MZ   benzyl   250    4    58   neutralization and                   
           benzoate                  salting-out                          
31   2MZ   dibenzyl 250    6    50   neutralization and                   
           terephthalate             salting-out                          
32   2MZ   dibenzyl 250    4    73   neutralization and                   
           isophthalate              salting-out                          
33   2IZ   tribenzyl                                                      
                    250    4    78   drying to solid and                  
           trimellitate              extraction with metha-               
                                     nol after neutralization             
34   2E4MZ dibenzyl 250    4    72   neutralization and                   
           succinate                 salting-out                          
__________________________________________________________________________
 
    
     REFERENTIAL EXAMPLE 1 
     Curing performances of 1-benzylimidazole compounds to liquid polyepoxy resins were examined. 
     A predetermined amount of a 1-benzylimidazole compound obtained according to the present invention was added as a curing agent to 100 parts by weight of a polyepoxy resin (Epikote #828 supplied by Yuka-Shell Epoxy), and the composition was cast into a space of 3 mm between two glass sheets. The case composition was maintained at 100° C., and the temperature was elevated to 150° C. and heating was conducted for 4 hours to effect curing. 
     The storage stability and gel time of each composition and the properties of the cured product were examined. The obtained results are shown in Table 3. 
     
                                           TABLE 3                                 
__________________________________________________________________________
 ##STR14##                                                                
                ##STR15##                                                 
__________________________________________________________________________
Amount (parts by weight)                                                  
               10     3     5     10                                      
Storage Stability*.sup.1                                                  
               1.09   7.44  1.65  1.27                                    
Gel Time       8&#39;26&#34;  2&#39;18&#34; 3&#39;58&#34; 2&#39;36&#34;                                   
(hot plate method, 150° C.)                                        
Glass Transition                                                          
               147    131   119   131                                     
Temperature                                                               
(TMA method, °C.)                                                  
Linear Expansion                                                          
               61 × 10.sup.-6                                       
                      72 × 10.sup.-6                                
                            72 × 10.sup.-6                          
                                  69 × 10.sup.-6                    
Coefficient (deg.sup.-1, 25° C.)                                   
Volume Resistivity                                                        
               8 × 10.sup.15                                        
                      2 × 10.sup.15                                 
                            5 × 10.sup.15                           
                                  2 × 10.sup.15                     
(Ω · cm, 25° C.)                                    
Dielectric Constant                                                       
               2.93   3.04  3.71  3.23                                    
(60Hz, 25° C.)                                                     
Dielectric Loss (60Hz,                                                    
               0.24   0.37  0.54  0.54                                    
25° C., %)                                                         
Flexural Strength                                                         
               7.1    6.6   7.9   11.1                                    
(Kgf/cm.sup.2, 25° C.)                                             
Flexural Modulus                                                          
               361    290   332   297                                     
(Kgf/cm.sup.2, 25° C.)                                             
Boiling Water Absorption                                                  
               0.99   0.86  0.72  0.80                                    
(8 hours&#39; boiling, % by                                                   
weight)                                                                   
__________________________________________________________________________
 Note                                                                     
 .sup.*1 ratio of viscosity of composition after standing for 24 hours at 
 25° C. to initial value of viscosity                              
 
    
     REFERENTIAL EXAMPLE 2 
     Curing-promoting performances of 1-benzylimidazole compounds to acid anhydrides were examined. 
     A composition comprising 100 parts by weight of a polyepoxy resin (#Epikote #828 supplied by Yuka-Shell Epoxy), 87.4 parts by weight methyl-Δ 4  -tetrahydrophthalic anhydride (Epichlon B570 supplied by Dai-Nippon Ink Kagaku Kogyo) and 0.5 part by weight of an imidazole compound was cast in a space of 3 mm between two glass sheets. The cast composition was maintained at 100° C. for 2 hours, and the temperature was elevated to 150° C. and the composition was heated for 4 hours to effect curing. 
     The storage stability and gel time of each composition and the properties of the cured product were examined. The obtained results are shown in Table 4. 
     The presence of a gelatinous substance (the salt of the acid anhydride with the imidazole) was not found in any composition. 
     
                                           TABLE 4                                 
__________________________________________________________________________
 ##STR16##                                                                
                ##STR17##                                                 
__________________________________________________________________________
Storage Stability.sup.*1                                                  
               2.71   4.33  2.61  2.60                                    
Gel Time.sup.*2                                                           
               19&#39;30&#34; 17&#39;24&#34;                                              
                            16&#39;39&#34;                                        
                                  18&#39;18&#34;                                  
Glass Transition                                                          
               126    129   120   122                                     
Temperature (TMA method,                                                  
°C.)                                                               
Linear Expansion Coeffi-                                                  
               65 × 10.sup.-6                                       
                      59 × 10.sup.-6                                
                            66 × 10.sup.-6                          
                                  58 × 10.sup.-6                    
cient (deg.sup.-1, 25° C.)                                         
Volume Resistivity                                                        
               2 × 10.sup.16                                        
                      1 × 10.sup.16                                 
                            4 × 10.sup.15                           
                                  7 × 10.sup.15                     
(Ω · cm, 25° C.)                                    
Dielectric Constant                                                       
               2.91   2.82  3.57  3.13                                    
(60Hz, 25° C.)                                                     
Dielectric Loss                                                           
               0.53   0.58  0.84  0.74                                    
(60Hz, 25° C., %)                                                  
Flexural Strength                                                         
               14.5   13.6  13.2  13.8                                    
(Kgf/cm.sup.2, 25° C.)                                             
Flexural Modulus                                                          
               349    318   327   371                                     
(Kgf/cm.sup.2, 25° C.)                                             
Boiling Water Absorption                                                  
               0.64   0.73  0.53  0.57                                    
(4 hours&#39; boiling, % by                                                   
weight)                                                                   
__________________________________________________________________________
 Note                                                                     
 .sup.*1 ratio of viscosity after standing at 40° C. for 24 hours t
 initial value of viscosity                                               
 .sup.*2 time required for stopping of rotational viscometer when         
 composition was maintained at 120° C.